Does a water damaged audio board mean no speaker?

I'm trying to repair a Macbook 12-inch 2016 I bought second hand. The seller said it was in his bag and some water was spilt in his bag.

The symptoms are:

- no speaker recognised by OS X

- headphone jack not working.

- microphone not recognised

I opened it up and I found the audio board looking water damaged but I cleaned it entirely with isopropanol 99% and I can't see any sign of water damage on it now.

The only water-damage sensors that are red are the one on the audio board and the one right before it (half way toward the front of the laptop, which suggests that the macbook was standing vertically on it right side (the audio jack side) when the water was spilt.

There is no sign of water damaged on the logic board or on the cables linking the right speaker to the logic board

My questions are:

-Are the speakers independent from the audio board?

-The right speaker itself may have been damaged, but why is the left speaker not working?

Any clue on what went wrong after the water damage?